Allow multiple reshares without root

Follow-up for #7578

Fixes #7587

app/models/reshare.rb

@@ -6,7 +6,7 @@ class Reshare < Post
   belongs_to :root, class_name: "Post", foreign_key: :root_guid, primary_key: :guid, optional: true
   validate :root_must_be_public
   validates_presence_of :root, :on => :create
-  validates_uniqueness_of :root_guid, :scope => :author_id
+  validates :root_guid, uniqueness: {scope: :author_id}, allow_nil: true
   delegate :author, to: :root, prefix: true
 
   before_validation do

spec/models/reshare_spec.rb

@@ -3,6 +3,7 @@ describe Reshare, type: :model do
     expect(FactoryGirl.build(:reshare)).to be_valid
   end
 
+  context "validation" do
     it "requires root" do
       reshare = FactoryGirl.build(:reshare, root: nil)
       expect(reshare).not_to be_valid
@@ -14,6 +15,31 @@ describe Reshare, type: :model do
       expect(reshare.errors[:base]).to include("Only posts which are public may be reshared.")
     end
 
+    it "allows two reshares without a root" do
+      reshare1 = FactoryGirl.create(:reshare, author: alice.person)
+      reshare2 = FactoryGirl.create(:reshare, author: alice.person)
+
+      reshare1.update_attributes(root_guid: nil)
+
+      reshare2.root_guid = nil
+      expect(reshare2).to be_valid
+    end
+
+    it "doesn't allow to reshare the same post twice" do
+      post = FactoryGirl.create(:status_message, public: true)
+      FactoryGirl.create(:reshare, author: alice.person, root: post)
+
+      expect(FactoryGirl.build(:reshare, author: alice.person, root: post)).not_to be_valid
+    end
+
+    it "allows to reshare the same post with different people" do
+      post = FactoryGirl.create(:status_message, public: true)
+      FactoryGirl.create(:reshare, author: alice.person, root: post)
+
+      expect(FactoryGirl.build(:reshare, author: bob.person, root: post)).to be_valid
+    end
+  end
+
   it "forces public" do
     expect(FactoryGirl.create(:reshare, public: false).public).to be true
   end